Next Generation Lunar Laser Ranging Alix Preston*, Stephen Merkowitz, Jan McGarry, Thomas Zagwodzki LUNAR Steering Committee Meeting April 12, 2011 *supported in part by an appointment to the NASA Posdoctoral Program at Goddard Space Flight Center, administered by Oak Ridge Associated Universities through contract with NASA

2 Lunar Ranging – LUNAR Steering Committee Meeting – 9/21/09 Hydroxide Bonding and Hollow Cubes GSFC has been investigating in-house hollow corner cube development Attempting to use Hydroxide-Bonding techniques to bond mirrors – Easy: only need a small amount of hydroxide solution (typically KOH or sodium silicate) – Strong: >1 MPa in shear – Can bond large surface areas – Works with a variety of materials – Can survive large temperature changes Currently understanding how the hydroxide bond cures – How much does it change the angles between surfaces? Two 1” mirrors bonded using the hydroxide bonding method

3 Lunar Ranging – LUNAR Steering Committee Meeting – 9/21/09 Current Work 6-axis piezo positioners that will be used to construct hollow corner cubes 1” corner cube produced using the piezo aligners and hydroxide bonding Fabricated fixture to make corner cubes – Can accommodate larger facets already 2” fused silica facet flats have been ordered (arrive in May) – Alignment procedures/test protocols will be established once the cubes are made – Zerodur facets will be ordered when this is completed Optimizing the bonding process is underway – a few variations have been found already Improvements were made to the far-field test bed – Transmit /receive optics simplified, fiber replaced spatial filter, larger off axis parabola with longer focal length, others

4 Lunar Ranging – LUNAR Steering Committee Meeting – 9/21/09 Future Work Plan Finish improvements to far-field test bed (almost done) Make and test 2” cubes – Attempt to have first cube made in June – Determine how the FFDP changes after thermally cycling – Compare cubes using different bonding methods Prepare report on 2” cubes Procure 5”-6” facets – Currently looking into possible vendors Make and test larger corner cubes Prepare report on larger cube results FFDP of an optical flat (left) and spare LAGOES 2 corner cube (right) using the improved setup. Quality is limited by air currents and vibrations Construction of the light-tight enclosure to reduce air turbulence